Devices for delivering a beneficial agent, such as a drug, to a fluid environment of use are known to the prior art. For example, U.S. Pat. No. 3,845,770 issued to Theeuwes and Higuchi and in U.S. Pat. No. 3,916,899, issued to the same patentees, an osmotic device is disclosed comprising a semipermeable wall that surrounds a compartment containing a beneficial agent. The wall is permeable to the passage of an external fluid and there is a passageway through the wall for delivering the beneficial agent from the device. These devices release the beneficial agent by fluid being imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall to produce an aqueous solution of the beneficial agent that is dispensed through the passageway from the device. These devices are extraordinarily effective for delivering a beneficial agent that is soluble in the aqueous fluid that exhibits an osmotic pressure gradient across the wall against the fluid. The devices are effective also for delivering a beneficial agent admixed with an osmotically effective solute that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against an aqueous fluid.
A quantum improvement in osmotic devices was presented to the pharmaceutical dispensing art by invention Theeuwes in U.S. Pat. Nos. 4,111,202; 4,111,203 and 4,203,439. In these patents the delivery kinetics of the device were enhanced for delivering a beneficial agent with degrees of solubility in an aqueous fluid. The kinetics are improved by manufacturing the device with a beneficial agent compartment and an osmotic compartment separated by a film. The devices deliver the beneficial agent by fluid being imbibed through the wall into the osmagent compartment producing a solution that causes the film to move and act as a driving force. The driving force pushes the beneficial agent through a passageway from the device.
A pioneer advancement in osmotic delivery devices was made by Cortese and Theeuwes in U.S. Pat. No. 4,327,725 and by Wong, Barclay, Deters and Theeuwes in U.S. Pat. No. 4,612,008. The osmotic devices disclosed in these patents comprise a semipermeable wall that surrounds a compartment. The compartment contains a beneficial agent formulation and an expandable hydrogel. In operation, fluid is imbibed into the compartment wherein it contacts the beneficial agent formulation thereby forming a dispensable formulation, and it contacts the hydrogel causing it to expand and push the dispensable formulation from the device.
The delivery devices described in the above presented patents operate successfully for their intended use and they deliver many difficult to deliver beneficial agents for their intended effect. Now, it has been observed their use can be limited because beneficial agents that are sensitive to aqueous biological fluids, or other fluid external to the delivery device, may be adversely effected by fluid imbibed into the compartment that contacts the beneficial agent during operation of the device. Examples of such sensitive agents include proteins and peptides.
It will be appreciated by those versed in the dispensing art that if a delivery device is provided for delivering a beneficial agent sensitive to aqueous fluids at a controlled rate, such a device would have a positive value and represent an advancement in the dispensing art. Likewise, it will be immediately appreciated by those versed in the dispensing art that if a delivery device is made available comprising means for protecting an aqueous sensitive beneficial agent, and which device possesses the thermodynamic ability to deliver the protected beneficial agent at a controlled rate, such a device would have a practical application in the fields of human and veterinary medicine.